Phase I will be devoted to learning techniques of molecular biology by joining Theodore Friedmann's ongoing studies of the introduction of foreign genes into mammalian cells. Courses and seminars in mammalian genetics will be attended at the University of California, San Diego; Scripps Clinic and Research Foundation; Salk Institute; and Agouron Institute. The goal of the initial research will be to increase the efficiency and safety of currently available retroviral vectors that have expressed the human HPRT gene in a variety of rodent and human cell lines. The mechanisms and sites of integration by the retroviral vectors will be studied. In addition, the ability of these vectors to transform rodent stem cells into expressing the human HPRT will be tested. These transformed stem cells will then be reintroduced into irradiated mice by transfusion and the in vivo expression of the human HPRT will be detected by several techniques, including immunochemical methods. During phase II, the molecular genetic basis of the PCC deficiency in propionic acidemia will be explored. The genes for the two subunits of PCC will be cloned. Southern and Northern blotting experiments will be done to characterize the genetic defect. Using the vectors developed in phase I, the PCC gene will be expressed in the bone marrow cells of patients with propionic acidemia.